1. Field of Invention
The present invention relates to the field of withdrawing material from a tank or conduit. In particular, the invention relates to valves for withdrawing material from tanks or conduits where there is a desire for valves that passively drain with a minimum of material hold-up and/or valves where seal change-out can be performed with minimal valve disassembly. (NOTE: While these valves may be designed as “drain” valves, they can be used with equal effectiveness on the side walls of tanks, in process flow lines as well as many other places in the process.) The invention also relates to the desire for equipment to be user-friendly, both at the outset when it is being installed, as well as when it is in use and, later, when equipment usage needs change. Optimally, equipment would lend itself to adaptation to new uses with minimal effort on the part of the owner or operator.
2. Description of Related Art
Many valves provide a means for draining the contents of a tank or conduit. However, these valves include a seal between the actuating shaft and the valve body that is formed by a flexing diaphragm or a sliding o-ring or packing. The seal formed between the shaft and the valve body is mounted in the bottom wall of the valve body, behind a second non-process side of the bottom wall. The wall thickness between the first process side of the bottom wall and the second non-process side of the wall, where the seal is actually formed with the valve body, creates/results in/forms a low pooling area in the bottom of the valve body that cannot be drained because the valve body bottom wall immediately around the seal is higher then the seal itself. Furthermore, because this seal is formed in the bottom wall of the valve body, seal replacement is carried out on existing drain valve designs by removal of the actuator from its attachment point on the bottom exterior wall of the valve body. Actuator removal for diaphragm replacement also requires that the actuating shaft be removed. While actuator and actuator shaft removal is both time-consuming and expensive, it also requires that an allowance be made for a substantial amount of space about the installation site of the valve so that the shaft and actuator can be removed.
A valve design that minimizes material hold-up while allowing ease of diaphragm change-out is desirable. A seal that is changeable without actuator removal would be of increasing value as valve size increases and subassemblies become bigger and more unwieldy. Diaphragm change-out without actuator removal would also allow the valve-actuator assembly to be mounted with much less distance between the ground and the tank or conduit valve mounting point, also a desirable feature. Furthermore, in some cases where fast delivery and installation of the valve are necessary for speedy delivery of the tank to the end user, a valve body designed in two pieces where the upper valve body attachment flange is simple and quick to fabricate and, consequently, quick to ready for supply to the fabricator of the tank or conduit, is also desirable. Lastly, it would also be desirable if the overall valve design would allow a given upper valve body to be fit with a variety of configurations of lower valve body and actuator and, in a similar fashion, a given lower valve body and actuator to be mated with a variety of configurations of the upper valve body.